Raid controlled semiconductor storage device

ABSTRACT

Provided is a RAID controlled storage device of a serial attached small computer system interface/serial advanced technology attachment (PCI-Express) type, which provides data storage/reading services through a PCI-Express interface. The PCI-Express type storage device includes: a memory disk unit which includes a plurality of memory disks provided with a plurality of volatile semiconductor memories; a PCI-Express host interface unit which interfaces between the memory disk unit and a host; and a controller unit which adjusts synchronization of a data signal transmitted/received between the PCI-Express host interface unit and the memory disk unit to control a data transmission/reception speed between the PCI-Express host interface unit and the memory disk unit. The storage device can support a low-speed data processing speed for the host and simultaneously support a high-speed data processing speed for the memory disk unit, so that there are advantages in that the performance of the memory disk can be fully utilized to enable high-speed data processing in an existing interface environment.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related in some aspects to commonly-owned,co-pending application Ser. No. 12/758,937, entitled SEMICONDUCTORSTORAGE DEVICE”, filed on Apr. 13, 2010.

FIELD OF THE INVENTION

The present invention relates to a RAID controlled semiconductor storagedevice of a PCI-Express (PCI-e) type.

BACKGROUND OF THE INVENTION

As the need for more computer storage grows, more efficient solutionsare being sought. As is known, there are various hard disk solutionsthat store/read data in a mechanical manner as a data storage medium.Unfortunately, data processing speed associated with hard disks is oftenslow. Moreover, existing solutions still use interfaces that cannotcatch up with the data processing speed of memory disks havinghigh-speed data input/output performance as an interface between thedata storage medium and the host. Therefore, there is a problem in theexisting area in that the performance of the memory disk cannot beproperty utilized.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a raid controlled storagedevice of a PCI-Express (PCI-e) type that supports a low-speed dataprocessing speed for a host. Specifically, embodiments of this inventionprovide a RAID controller coupled to one or more (i.e., a set of)semiconductor storage devices (SSDs). Among other things, the SSDsadjust a synchronization of a data signal transmitted/received betweenthe host and a memory disk during data communications between the hostand the memory disk through a PCI-Express interface and simultaneouslysupport a high-speed data processing speed for the memory disk, therebysupporting the performance of the memory to enable high-speed processingin an existing interface environment at the maximum.

A first aspect of the present invention provides a RAID controlledsemiconductor storage device (SSD), comprising: an SSD memory disk unitcomprising a plurality of memory disks provided having a plurality ofsemiconductor memories; a RAID controller coupled to the SSD memory diskunit; a host interface unit which interfaces between the SSD memory diskunit and a host; and a controller unit coupled to the RAID controllerconfigured to adjust a synchronization of a data signal communicatedbetween the host interface unit and the SSD memory disk unit to controla communication speed between the host interface unit and the SSD memorydisk unit.

A second aspect of the present invention provides a RAID controlledPCI-Express type semiconductor storage device (SSD), comprising: an SSDmemory disk unit comprising a plurality of memory disks provided havinga plurality of volatile semiconductor memories; a RAID controllercoupled to the SSD memory disk unit; a PCI-Express host interface unitwhich interfaces between the SSD memory disk unit and a host; acontroller unit coupled to the RAID controller that adjusts asynchronization of a data signal communicated between the PCI-Expresshost interface unit and the SSD memory disk unit to control a datacommunication speed between the PCI-Express host interface unit and theSSD memory disk unit; and the controller unit comprising: a memorycontrol module which controls data input/output of the SSD memory diskunit; a DMA control module which controls the memory control module tostore data in the SSD memory disk unit or reads data from the SSD memorydisk unit to provide the data to the host, according to an instructionfrom the host received through the PCI-Express host interface unit; abuffer which buffers data according to control of the DMA controlmodule; and a synchronization control module for synchronizing acommunication speed of a data signal.

A third aspect of the present invention provides a method for providinga RAID controlled semiconductor storage device (SSD), comprising:providing a SSD memory disk unit comprising a plurality of memory disksprovided having a plurality of semiconductor memories; providing a RAIDcontroller coupled to the SSD memory disk unit; providing a hostinterface unit which interfaces between the SSD memory disk unit and ahost; and providing a controller unit coupled to the RAID controllerconfigured to adjust a synchronization of a data signal communicatedbetween the host interface unit and the SSD memory disk unit to controla communication speed between the host interface unit and the SSD memorydisk unit.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will be more readilyunderstood from the following detailed description of the variousaspects of the invention taken in conjunction with the accompanyingdrawings in which:

FIG. 1 is a diagram schematically illustrating a configuration of a RAIDcontrolled storage device of a PCI-Express (PCI-e) type according to anembodiment.

FIG. 2 is a more specific diagram of a RAID controller coupled to a setof SSDs.

FIG. 3 is a diagram schematically illustrating a configuration of thehigh speed SSD of FIG. 1.

FIG. 4 is a diagram schematically illustrating a configuration of acontroller unit in FIG. 1.

The drawings are not necessarily to scale. The drawings are merelyschematic representations, not intended to portray specific parametersof the invention. The drawings are intended to depict only typicalembodiments of the invention, and therefore should not be considered aslimiting the scope of the invention. In the drawings, like numberingrepresents like elements.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments now will be described more fully herein withreference to the accompanying drawings, in which exemplary embodimentsare shown. This disclosure may, however, be embodied in many differentforms and should not be construed as limited to the exemplaryembodiments set forth therein. Rather, these exemplary embodiments areprovided so that this disclosure will be thorough and complete and willfully convey the scope of this disclosure to those skilled in the art.In the description, details of well-known features and techniques may beomitted to avoid unnecessarily obscuring the presented embodiments.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of this disclosure.As used herein, the singular forms “a”, “an”, and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. Furthermore, the use of the terms “a”, “an”, etc. do notdenote a limitation of quantity, but rather denote the presence of atleast one of the referenced items. It will be further understood thatthe terms “comprises” and/or “comprising”, or “includes” and/or“including”, when used in this specification, specify the presence ofstated features, regions, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, regions, integers, steps, operations, elements,components, and/or groups thereof. Moreover, as used herein, the termRAID means redundant array of independent disks (originally redundantarray of inexpensive disks). In general, RAID technology is a way ofstoring the same data in different places (thus, redundantly) onmultiple hard disks. By placing data on multiple disks, I/O(input/output) operations can overlap in a balanced way, improvingperformance. Since multiple disks increase the mean time betweenfailures (MTBF), storing data redundantly also increases faulttolerance.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art. It will be further understood that termssuch as those defined in commonly used dictionaries should beinterpreted as having a meaning that is consistent with their meaning inthe context of the relevant art and the present disclosure, and will notbe interpreted in an idealized or overly formal sense unless expresslyso defined herein.

Hereinafter, a RAID storage device of a serial attached small computersystem interface/serial advanced technology attachment (PCI-Express)type according to an embodiment will be described in detail withreference to the accompanying drawings.

As indicated above, embodiments of the present invention provide a RAIDcontrolled storage device of a serial attached small computer systeminterface/serial advanced technology attachment (PCI-Express) type thatsupports a low-speed data processing speed for a host. This is typicallyaccomplished by adjusting a synchronization of a data signaltransmitted/received between the host and a memory disk during datacommunications between the host and the memory disk through aPCI-Express interface and by simultaneously supporting a high-speed dataprocessing speed for the memory disk, thereby supporting the performanceof the memory to enable high-speed processing in an existing interfaceenvironment at the maximum.

The storage device of a serial attached small computer systeminterface/serial advanced technology attachment (PCI-Express) typesupports a low-speed data processing speed for a host by adjustingsynchronization of a data signal transmitted/received between the hostand a memory disk during data communications between the host and thememory disk through a PCI-Express interface, and simultaneously supportsa high-speed data processing speed for the memory disk, therebysupporting the performance of the memory to enable high-speed dataprocessing in an existing interface environment at the maximum. It isunderstood in advance that although PCI-Express technology will beutilized in a typical embodiment, other alternatives are possible. Forexample, the present invention could utilize SAS/SATA technology inwhich a SAS/SATA type storage device is provided that utilizes aSAS/SATA interface.

Referring now to FIG. 1, a diagram schematically illustrating aconfiguration of a PCI-Express type, RAID controlled storage device(e.g., for providing storage for a serially attached computer device)according to an embodiment of the invention is shown. As depicted, FIG.1 shows a RAID controlled PCI-Express type storage device according toan embodiment of the invention which includes a memory disk unit 100comprising: a plurality of memory disks having a plurality of volatilesemiconductor memories (also referred to herein as high speed SSDs 100);a RAID controller 800 coupled to SSDs 100; an interface unit 200 (e.g.,PCI-Express host) which interfaces between the memory disk unit and ahost; a controller unit 300; an auxiliary power source unit 400 that ischarged to maintain a predetermined power using the power transferredfrom the host through the PCI-Express host interface unit; a powersource control unit 500 that supplies the power transferred from thehost through the PCI-Express host interface unit to the controller unit,the memory disk unit, the backup storage unit, and the backup controlunit which, when the power transferred from the host through thePCI-Express host interface unit is blocked or an error occurs in thepower transferred from the host, receives power from the auxiliary powersource unit and supplies the power to the memory disk unit through thecontroller unit; a backup storage unit 600 that stores data of thememory disk unit; and a backup control unit 700 that backs up datastored in the memory disk unit in the backup storage unit, according toan instruction from the host or when an error occurs in the powertransmitted from the host.

The memory disk unit 100 includes a plurality of memory disks providedwith a plurality of volatile semiconductor memories for high-speed datainput/output (for example, DDR, DDR2, DDR3, SDRAM, and the like), andinputs and outputs data according to the control of the controller 300.The memory disk unit 100 may have a configuration in which the memorydisks are arrayed in parallel.

The PCI-Express host interface unit 200 interfaces between a host andthe memory disk unit 100. The host may be a computer system or the like,which is provided with a PCI-Express interface and a power source supplydevice.

The controller unit 300 adjusts synchronization of data signalstransmitted/received between the PCI-Express host interface unit 200 andthe memory disk unit 100 to control a data transmission/reception speedbetween the PCI-Express host interface unit 200 and the memory disk unit100.

Referring now to FIG. 2, a more detailed diagram of a RAID controlledSSD 810 is shown. As depicted, a PCI-e type RAID controller 800 can bedirectly coupled to any quantity of SSDs 100. Among other things, thisallows for optimum control of SSDs 100. Among other things, the use of aRAID controller 800:

-   -   1. Supports the current backup/restore operations.    -   2. Provides additional and improved backup function by        performing the following:        -   a) The internal backup controller determines the backup            (user's request order or the status monitor detects power            supply problems);        -   b) The internal backup controller requests a data backup to            SSDs;        -   c) The internal backup controller requests internal backup            device to backup data immediately;        -   d) Monitors the status of the backup for the SSDs and            internal backup controller; and        -   e) Reports the internal backup controller's status and            end-op.    -   3. Provides additional and improved restore function by        performing the following:        -   a) The internal backup controller determines the restore            (user's request order or the status monitor detects power            supply problems);        -   b) The internal backup controller requests a data restore to            the SSDs;        -   c) The internal backup controller requests internal backup            device to restore data immediately;        -   d) Monitors the status of the restore for the SSDs and            internal backup controller; and        -   e) Reports the internal backup controller status and end-op.

Referring now to FIG. 3, a diagram schematically illustrating aconfiguration of the high speed SSD 100 is shown. As depicted,SSD/memory disk unit 100 comprises: a host interface 202 (e.g.,PCI-Express host) (which can be interface 200 of FIG. 1, or a separateinterface as shown); a DMA controller 302 interfacing with a backupcontrol module 700; an ECC controller; and a memory controller 306 forcontrolling one or more blocks 604 of memory 602 that are used ashigh-speed storage.

FIG. 4 is a diagram schematically illustrating a configuration of thecontroller unit provided in the PCI-Express type storage deviceaccording to the embodiment. Referring to FIG. 4, the controller unit300 according to the embodiment includes: a memory control module 310which controls data input/output of the memory disk unit 100; a DMA(Direct Memory Access) control module 320 which controls the memorycontrol module 310 to store the data in the memory disk unit 100, orreads data from the memory disk unit 100 to provide the data to thehost, according to an instruction from the host received through thePCI-Express host interface unit 200; a buffer 330 which buffers dataaccording to the control of the DMA control module 320; asynchronization control module 340 which, when receiving a data signalcorresponding to the data read from the memory disk unit 100 by thecontrol of the DMA control module 320 through the DMA control module 320and the memory control module 310, adjusts synchronization of a datasignal so as to have a communication speed corresponding to aPCI-Express communications protocol to transmit the synchronized datasignal to the PCI-Express host interface unit 200, and when receiving adata signal from the host through the PCI-Express host interface unit200, adjusts synchronization of the data signal so as to have atransmission speed corresponding to a communications protocol (forexample, PCI, PCI-x, or PCI-e, and the like) used by the memory diskunit 100 to transmit the synchronized data signal to the memory diskunit 100 through the DMA control module 320 and the memory controlmodule 310; and a high-speed interface module 350 which processes thedata transmitted/received between the synchronization control module 340and the DMA control module 320 at high speed. Here, the high-speedinterface module 350 includes a buffer having a double buffer structureand a buffer having a circular queue structure and processes the datatransmitted/received between the synchronization control module 340 andthe DMA control module 320 without loss at high speed by buffering thedata transmitted/received between the synchronization control module 340and the DMA control module 320 using the buffers and adjusting dataclocks.

The auxiliary power source unit 400 may be configured as a rechargeablebattery or the like, so that it is normally charged to maintain apredetermined power using power transferred from the host through thePCI-Express host interface unit 200 and supplies the charged power tothe power source control unit 500 according to the control of the powersource control unit 500.

The power source control unit 500 supplies the power transferred fromthe host through the PCI-Express host interface unit 200 to thecontroller unit 300, the memory disk unit 100, the backup storage unit600, and the backup control unit 700.

In addition, when an error occurs in a power source of the host becausethe power transmitted from the host through the PCI-Express hostinterface unit 200 is blocked, or the power transmitted from the hostdeviates from a threshold value, the power source control unit 500receives power from the auxiliary power source unit 400 and supplies thepower to the memory disk unit 100 through the controller unit 300.

The backup storage unit 600 is configured as a low-speed non-volatilestorage device such as a hard disk and stores data of the memory diskunit 100.

The backup control unit 700 backs up data stored in the memory disk unit100 in the backup storage unit 600 by controlling the data input/outputof the backup storage unit 600 and backs up the data stored in thememory disk unit 100 in the backup storage unit 600 according to aninstruction from the host, or when an error occurs in the power sourceof the host due to a deviation of the power transmitted from the hostdeviates from the threshold value.

While the exemplary embodiments have been shown and described, it willbe understood by those skilled in the art that various changes in formand details may be made thereto without departing from the spirit andscope of this disclosure as defined by the appended claims. In addition,many modifications can be made to adapt a particular situation ormaterial to the teachings of this disclosure without departing from theessential scope thereof. Therefore, it is intended that this disclosurenot be limited to the particular exemplary embodiments disclosed as thebest mode contemplated for carrying out this disclosure, but that thisdisclosure will include all embodiments falling within the scope of theappended claims.

The RAID controlled storage device of a serial attached small computersystem interface/serial advanced technology attachment (PCI-Express)type supports a low-speed data processing speed for a host by adjustingsynchronization of a data signal transmitted/received between the hostand a memory disk during data communications between the host and thememory disk through a PCI-Express interface and simultaneously supportsa high-speed data processing speed for the memory disk, therebysupporting the performance of the memory to enable high-speed dataprocessing in an existing interface environment at the maximum.

The foregoing description of various aspects of the invention has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed and, obviously, many modifications and variations arepossible. Such modifications and variations that may be apparent to aperson skilled in the art are intended to be included within the scopeof the invention as defined by the accompanying claims.

What is claimed is:
 1. A RAID controlled semiconductor storage device(SSD), comprising: an SSD memory disk unit comprising a plurality ofmemory disks provided having a plurality of semiconductor memories; aRAID controller coupled to the SSD memory disk unit; and a controllerunit coupled to the RAID controller configured to adjust asynchronization of a data signal communicated between a host interfaceunit and the SSD memory disk unit to control a communication speedbetween the host interface unit and the SSD memory disk unit, whereinthe controller unit comprises: a memory control module for controllingdata input/output of the SSD memory disk unit; a DMA control modulewhich controls the memory control module to store data in the SSD memorydisk unit or reads data from the SSD memory disk unit to provide thedata to the host according to an instruction from the host receivedthrough the host interface unit; a buffer which buffers data accordingto control of the DMA control module; a synchronization control modulewhich, when receiving a data signal corresponding to the data read fromthe SSD memory disk unit by the control of the DMA control modulethrough the DMA control module and the memory control module, adjustssynchronization of a data signal so as to have a communication speedcorresponding to a PCI-Express communications protocol to transmit thesynchronized data signal to the PCI-Express host interface unit and,when receiving a data signal from the host through the PCI-Express hostinterface unit, adjusts synchronization of the data signal so as to havea transmission speed corresponding to a communications protocol used bythe SSD memory disk unit to transmit the synchronized data signal to theSSD memory disk unit through the DMA control module and the memorycontrol module; and a high-speed interface module which processes thedata transmitted/received between the synchronization control module andthe DMA control module at high speed, including a buffer having a doublebuffer structure and a buffer having a circular queue structure, andprocesses the data transmitted/received between the synchronizationcontrol module and the DMA control without loss of high speed bybuffering the data transmitted/received between the synchronizationcontrol module and the DMA control module using the buffers andadjusting data clocks.
 2. The RAID controlled SSD of claim 1, furthercomprising: a backup storage unit which stores data of the SSD memorydisk unit; and a backup control unit which backs up data stored in theSSD memory disk unit in the backup storage unit, according to aninstruction from the host or when an error occurs in the powertransmitted from the host.
 3. The RAID controlled SSD of claim 2,further comprising: an auxiliary power source unit which is charged tomaintain a predetermined power using the power transferred from the hostthrough the host interface unit; and a power source control unit whichsupplies the power transferred from the host through the host interfaceunit to the controller unit, the SSD memory disk unit, the backupstorage unit, and the backup control unit and, when the powertransferred from the host through the host interface unit is blocked oran error occurs in the power transferred from the host, receives powerfrom the auxiliary power source unit and supplies the power to thememory disk unit through the controller unit.
 4. The RAID controlled SSDof claim 1, the plurality of semiconductor memories being volatile, andthe host interface unit being a PCI-Express host interface unit.
 5. TheRAID controlled SSD of claim 1, the SSD memory disk unit comprising: aDMA controller coupled to the host interface unit; an ECC controllercoupled to the DMA controller; a memory controller coupled to the ECCcontroller; and a memory array coupled to the memory controller, thememory array comprising at least one memory block.
 6. The RAIDcontrolled SSD of claim 1, the SSD memory disk unit providing storagefor a serially attached computer device.
 7. A PCI-Express type RAIDcontrolled semiconductor storage device (SSD), comprising: a SSD memorydisk unit comprising a plurality of memory disks having a plurality ofvolatile semiconductor memories; a RAID controller coupled to the SSDmemory disk unit; a PCI-Express host interface unit which interfacesbetween the SSD memory disk unit and a host; a controller unit coupledto the RAID controller that adjusts a synchronization of a data signalcommunicated between the PCI-Express host interface unit and the SSDmemory disk unit to control a data communication speed between thePCI-Express host interface unit and the SSD memory disk unit; and thecontroller unit comprising: a memory control module which controls datainput/output of the SSD memory disk unit; a DMA control module whichcontrols the memory control module to store data in the SSD memory diskunit or reads data from the SSD memory disk unit to provide the data tothe host, according to an instruction from the host received through thePCI-Express host interface unit; a buffer which buffers data accordingto control of the DMA control module; and a synchronization controlmodule for synchronizing a communication speed of a data signal, whereinthe synchronization control module is configured to: when receiving adata signal corresponding to the data read from the SSD memory disk unitby the control of the DMA control module through the DMA control moduleand the memory control module, adjust a synchronization of a data signalso as to have a communication speed corresponding to a PCI-Expresscommunications protocol to transmit the synchronized data signal to thePCI-Express host interface unit; and when receiving a data signal fromthe host through the PCI-Express host interface unit, adjustsynchronization of the data signal so as to have a transmission speedcorresponding to a communications protocol used by the SSD memory diskunit to transmit the synchronized data signal to the SSD memory diskunit through the DMA control module and the memory control module; and ahigh-speed interface module which processes the datatransmitted/received between the synchronization control module and theDMA control module at high speed.
 8. The PCI-Express type SSD of claim7, further comprising: a backup storage unit which stores data of theSSD memory disk unit; and a backup control unit which backs up datastored in the SSD memory disk unit in the backup storage unit, accordingto an instruction from the host or when an error occurs in the powertransmitted from the host.
 9. The PCI-Express type SSD of claim 7,further comprising: an auxiliary power source unit which is charged tomaintain a predetermined power using the power transferred from the hostthrough the PCI-Express host interface unit; and a power source controlunit which supplies the power transferred from the host through thePCI-Express host interface unit to the controller unit, the SSD memorydisk unit, the backup storage unit, and the backup control unit and,when the power transferred from the host through the PCI-Express hostinterface unit is blocked or an error occurs in the power transferredfrom the host, receives power from the auxiliary power source unit andsupplies the power to the SSD memory disk unit through the controllerunit.
 10. The PCI-Express type SSD of claim 7, the SSD memory disk unitproviding storage for a serially attached computer device.
 11. A methodfor providing a RAID controlled semiconductor storage device (SSD),comprising: providing an SSD memory disk unit comprising a plurality ofmemory disks provided having a plurality of semiconductor memories;providing a RAID controller coupled to the SSD memory disk unit;providing a host interface unit which interfaces between the SSD memorydisk unit and a host; and providing a controller unit coupled to theRAID controller configured to adjust a synchronization of a data signalcommunicated between a host interface unit and the SSD memory disk unitto control a communication speed between the host interface unit and theSSD memory disk unit, wherein the providing of the controller unitcomprises: providing a memory control module for controlling datainput/output of the SSD memory disk unit; providing a DMA control modulewhich controls the memory control module to store data in the SSD memorydisk unit or reads data from the SSD memory disk unit to provide thedata to the host, according to an instruction from the host receivedthrough the host interface unit; providing a buffer which buffers dataaccording to control of the DMA control module; providing asynchronization control module which, when receiving a data signalcorresponding to the data read from the SSD memory disk unit by thecontrol of the DMA control module through the DMA control module and thememory control module, adjusts synchronization of a data signal so as tohave a communication speed corresponding to a PCI-Express communicationsprotocol to transmit the synchronized data signal to the PCI-Expresshost interface unit and, when receiving a data signal from the hostthrough the PCI-Express host interface unit, adjusts synchronization ofthe data signal so as to have a transmission speed corresponding to acommunications protocol used by the SSD memory disk unit to transmit thesynchronized data signal to the SSD memory disk unit through the DMAcontrol module and the memory control module; and providing a high-speedinterface module which processes the data transmitted/received betweenthe synchronization control module and the DMA control module at highspeed and includes a buffer having a double buffer structure and abuffer having a circular queue structure, and processes the datatransmitted/received between the synchronization control module and theDMA control without loss of high speed by buffering the datatransmitted/received between the synchronization control module and theDMA control module using the buffers and adjusting data clocks.
 12. Themethod of claim 11, further comprising: providing a backup storage unitwhich stores data of the SSD memory disk unit; and providing a backupcontrol unit which backs up data stored in the SSD memory disk unit inthe backup storage unit, according to an instruction from the host orwhen an error occurs in the power transmitted from the host.
 13. Themethod of claim 12, further comprising: providing an auxiliary powersource unit which is charged to maintain a predetermined power using thepower transferred from the host through the host interface unit; andproviding a power source control unit which supplies the powertransferred from the host through the host interface unit to thecontroller unit, the SSD memory disk unit, the backup storage unit, andthe backup control unit and, when the power transferred from the hostthrough the host interface unit is blocked or an error occurs in thepower transferred from the host, receives power from the auxiliary powersource unit and supplies the power to the memory disk unit through thecontroller unit.
 14. The method of claim 11, the plurality ofsemiconductor memories being volatile.
 15. The method of claim 11, thehost interface unit being a PCI-Express host interface unit.
 16. Themethod of claim 11, the SSD memory disk unit providing storage for aserially attached computer device.